Kinetic applications of electron paramagnetic resonance spectroscopy. 42. Some reactions of the bis(trifluoromethyl)aminoxyl radical

Doba, Takahisa; Ingold, K. U.

doi:10.1021/ja00326a012

Cited by 43 publications

(31 citation statements)

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“…In works by both Connolly and Scaiano 121 and Opeida et al, 122 TEMPO abstracted activated hydrogen atoms at elevated temperatures. Electron-poor nitroxides such as bis(trifluoromethyl) nitroxide [123][124][125] and acyl nitroxide phthalimide N-oxyl (PINO) 126 readily abstract unactivated hydrogen atoms under ambient conditions. In an elegant set of experiments, Coseri, Mendenhall, and Ingold studied the propensity of nitroxides to abstract a secondary allylic hydrogen rather than add to a secondary olefin.…”

Section: Nitroxide Backgroundmentioning

confidence: 99%

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Nilsen

Braslau

2005

J. Polym. Sci. A Polym. Chem.

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ABSTRACT:Nitroxides bearing an a-hydrogen decompose upon heating in a bimolecular reaction. A new mechanism is proposed for the decomposition of t-butylisopropylphenyl nitroxide (TIPNO) involving the formation of a head-to-tail dimer, single electron transfer to form an oxammonium salt, epimerization to the corresponding nitrone, and elimination to form a conjugated oxime. This mechanism may provide insights into designing new nitroxides for use in controlled polymerization.

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Section: Nitroxide Backgroundmentioning

confidence: 99%

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Nilsen

Braslau

2005

J. Polym. Sci. A Polym. Chem.

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“…( Table 3) It is worth to point out that the reactivity of abstraction of benzylic hydrogens by the present aminoxyl radicals is substantially lower than that documented for other oxygen-centred radicals, [10,20,26] such as HO . or t-BuO .…”

Section: Characterization Of the Radical Tfnomentioning

confidence: 64%

“…1) in Freon. [20] We report here on the first generation of TFNO from the commercially available 6-CF 3 -1-hydroxy-benzotriazole (TFBT) precursor. Following the addition of a stoichiometric amount of the monoelectronic oxidant CAN (E° 1.3 V vs NHE) [18] (Fig.…”

Section: Characterization Of the Radical Tfnomentioning

confidence: 99%

“…[9,10,12,13] Kinetic surveys have been already performed with PINO or else with its X-aryl-substituted cognates, [13][14][15][16][17] and have been recently complemented by a kinetic investigation with another aminoxyl radical, that is benzotriazole N-oxyl (BTNO), [18] originating from precursor 1-hydroxybenzotriazole (HBT). [19] Another kinetic study had been reported with bis(trifluoromethyl)aminoxyl radical, [20] (CF 3 ) 2 N-O . (dubbed here BTFN).…”

Section: Introductionmentioning

confidence: 99%

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Hydrogen abstraction from H‐donor substrates by the 6‐CF₃‐benzotriazol‐N‐oxyl radical (TFNO)

Tadesse¹,

Galli²,

Gentili³

2010

J of Physical Organic Chem

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The aminoxyl radical 6-trifluoromethyl-benzotriazol-N-oxyl (TFNO) has been generated from the parent hydroxylamine 6-CF3-1-hydroxy-benzotriazole (TFBT) by one-electron oxidation with a Ce-IV salt and characterized by spectrophotometry and cyclic voltammetry (CV). Rate constants of H-abstraction (k(H)) by TFNO from a number of H-donor benzylic substrates have been determined spectrophotometrically in MeCN solution at 25 degrees C. A radical H-atom transfer (HAT) route of oxidation is substantiated for TFNO by several pieces of evidence. The kinetic data also testify the relevance of stereoelectronic effects upon the HAT reactivity of TFNO. Copyright (C) 2010 John Wiley & Sons, Ltd

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“…Follow-up work [27] revealed that the CF 3 OOCF 3 /(CF 3 ) 2 NOH method for generating (CF 3 ) 2 NO radicals that had been employed [25] had problems. This method necessarily involves low [(CF 3 ) 2 NO ]/[(CF 3 ) 2 NOH] ratios and not all R were trapped by (CF 3 ) 2 NO (e.g., reaction (28.22)).…”

Section: H-atom Abstraction By Methyl Radicals In Organic Glassesmentioning

confidence: 99%

Quantum Mechanical Tunneling of Hydrogen Atoms in Some Simple Chemical Systems

Ingold

2006

Hydrogen‐Transfer Reactions

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Not only is it difficult to prove that a given reaction proceeds via tunneling, it is even difficult to define the term tunneling unambiguously. The hydrogen atoms themselves, one presumes, are unaware that they are tunneling: from their vantage point the barrier is, like beauty, only present in the eye of the observer. Moreover, not all observers will see the barrier but only those that have not yet overcome their classical prejudices.Willem Siebrand 1984 IntroductionIn 1933 Bell [1] predicted that, due to quantum mechanical effects, the rate of transfer of a hydrogen atom (H-atom) or proton would become temperature independent at low temperatures. Since that time, kineticists have embraced the concept of quantum mechanical tunneling (QMT) so enthusiastically that it is frequently invoked on the flimsiest of experimental evidence, often using data obtained at, or above, room temperature. At such elevated temperatures, conclusive evidence that the rate of an H-atom or proton transfer is enhanced above that due to "over the top of the barrier" thermal activation, and can only be explained by there being a significant contribution from QMT, is rare. Significant has been italicized in the foregoing sentence because QMT will always make some contribution to the rate of such transfers. The QMT contribution to the transfer rate becomes more obvious at low temperatures. For this reason, the unequivocal identification of QMT in simple chemical systems requires that their rates of reaction be measured at low temperatures.In this chapter, a few simple unimolecular and bimolecular reactions will be described in which the rates of H-atom motion were measured down to very low temperatures. These kinetic measurements provide unequivocal evidence that QMT dominates the reaction rates over a wide range of temperatures. There are two common themes. First, all the experimental data were generated in my own Hydrogen-Transfer Reactions. Edited by

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Kinetic applications of electron paramagnetic resonance spectroscopy. 42. Some reactions of the bis(trifluoromethyl)aminoxyl radical

Cited by 43 publications

References 6 publications

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Hydrogen abstraction from H‐donor substrates by the 6‐CF₃‐benzotriazol‐N‐oxyl radical (TFNO)

Quantum Mechanical Tunneling of Hydrogen Atoms in Some Simple Chemical Systems

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Kinetic applications of electron paramagnetic resonance spectroscopy. 42. Some reactions of the bis(trifluoromethyl)aminoxyl radical

Cited by 43 publications

References 6 publications

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

Hydrogen abstraction from H‐donor substrates by the 6‐CF3‐benzotriazol‐N‐oxyl radical (TFNO)

Quantum Mechanical Tunneling of Hydrogen Atoms in Some Simple Chemical Systems

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Hydrogen abstraction from H‐donor substrates by the 6‐CF₃‐benzotriazol‐N‐oxyl radical (TFNO)